In this branch of his work the hydraulic engineer enters largely into the field of hydro mechanics as above defined, since he must study the mechanical effects which may be produced by utilizing the force exerted by water in mo tion to generate power. In hydraulic works, distinctively so called, the effort is constantly made to diminish the mechanical effect of the moving water so as to avoid injury to surfaces and substances unprepared to resist it. In hydrodynamic works the effort is made to con centrate all the power obtainable from the moving water and transmit it to machines which do effective work.
In the present state of hydraulic science more attention is being paid than ever before to the obtaining of closely accurate results of experiments conducted by skilled observers, in which the aid of electricity is used to register all phenomena in a manner never possible here tofore. Great as the advantages have been during the last 25 or 30 years, equal or greater progress in the elucidation and practical appli cation of principles may be expected within the next quarter of a century.
The least in present import ance to mankind but the first in historic de velopment of industries is the use of water in inland navigation. Railroads have increased to such an extent that the use of the rivers and lakes for transporting persons and products, while still important, is relatively far less so than in former years. Civilization can expand and succeed if there is an adequate supply of water for the purposes before mentioned, even if navigation is not employed, asgoods can be transported by rail with a high degree of economy. Up to the first half of the 19th however, water transportation was of prime importance as communication by land was slow and in places almost impracticable. On the other hand the relatively sparse popula tion and undeveloped condition of industries offered few hydraulic problems. It thus re sulted that in the Constitution of the United States, while the rights of navigation are pro tected, there is practically no provision made for other uses of water. What are now found to be the more pressing needs of communities in regard to water supply required for domestic and municipal purposes, for irrigation, for dis posal of wastes: for manufacturing or for power purposes — have come forward promi nently since the Constitution was adopted. Par ticularly with reference to interstate waters there is much uncertainty in Federal and State laws, hampering the work of the engineer.
Navigation upon the ocean is, of course, of vital importance to the nations of the world and hydraulic engineering works having to dd with harbors are being built of rapidly increas ing magnitude as the size of the ships increase. but with respect to the inland passages and rivers there has been rapid decline of their use in navigation, such that, outside of the opera tions of the corps of engineers of the United States army, few advances have been made.
There are indications, however, that a change is about to take place and that with the de velopment of different types of barge and of modified power boats, the rivers upon which navigation has practical13$ ceased will be more generally employed and there will he a larger demand for works for their regulation and control for purposes of navigation.
As a notable exception in the general decline of interest in inland navigation should be cited the expenditures being made in enlarging and changing the alignment of the Erie Canal from the vicinity of Buffalo, N. Y., east to Albany and the connecting canal to Lake Cham plain. Over $100,000,000 was appropriated by the legislature of New York State for chang ing the old waterway into a barge canal capable of navigation by boats drawing nine feet of water. Later appropriations have been made and notable hydraulic works executed. There have also been large expenditures made by the Federal government for the improvement of the channels connecting the Great Lakes. On these the conditions are more nearly comparable to ocean navigation; the freight traffic, prin cipally of iron ore, coal and grain on Sault Sainte Marie and Detroit River surpasses that of the Suez Canal.
An interesting and important branch of hydraulic engineering is that which deals with larger masses of water than any of those so far considered. Along the sea-coasts of all countries there are places where the con formation of the shore and the nature of the contiguous lands render the creation of harbors desirable, but where the tidal waves and littoral currents come in conflict in such a way as to make the approach from the sea dangerous to vessels. To lessen the destructive effects of the Feat masses of water in motion, impelled by either the wind or the tidal currents, break waters or piers of stone projecting from the shore are built with good results. The massive ness which such structures are required to possess may be judged from the fact that it has been learned that the foundation for a break water must extend out to where there is from 18 to 20 feet of water at low tide; that the height of the waves by which it is likely to be assailed may be from 10 to 20 feet ; and that the impact of the wave on the opposing struc ture may be as high as 6,000 pounds to the square foot. In the open sea it is not likely that waves as high as this are formed, or that the fcrce exerted by them is nearly as great, but the problem of the form and resisting power of the hull of ships has to be considered from the standpoint of the dynamic effect of the water which is impelled by the wind and waves against the hull, as well as the resistance offered by the water to the passage of the hull through it.